272 



NA I U!:e 



[J A 



1908 



tion of the individual grains as separate particles, because 

 the contact of one grain with another would prevent such 

 vibrations, and suggested that the only other explanation 

 possible was that certain grains, in rubbing one against 

 another, might produce the required vibrations through 

 surface friction. 



The music from sands is a cumulative effect, and only 

 possible under the prevalence of numerous favourable con- 

 ditions, and I found that if I eliminated one apparently 

 insignificant factor from the conditions upon which my 

 theory was based, the production of musical sands 

 artificially became impossible. 



Until an artificial musical sand can be produced ex- 

 clusively under the conditions suggested by Profs. Poynting 

 and Thomson in "Sound," I submit that my explanation 

 may be retained. Cecil Carus-Wilson. 



Filtration of Rain Water. 



I WISH to ask the opinion of someone in regard to the 

 filtration of rain water, and the removal of any sediment, 

 before it finds its way into large underground cisterns 

 holding fully 15,000 gallons. 



It will not be difficult or costly to collect the water and 

 pump it up for use in a large laundry. A pump can be 

 worked by the engine close by. 



The point is how to prevent a lot of smuts, &c., finding 

 their way into the cisterns, which would necessitate the 

 frequent removal of this stuff, an operation that would 

 be both difficult and expensive. 



Is there any way by which filtration can be carried out 

 above ground? 



I shall be glad to know of any way to meet the difficulty. 



January 13. Enquirer. 



THE HIGHLAND OVERTHRUSTS.' 

 'T'HE controversy regarding the structure of the 

 ■^ north-western Highlands was a disturbing 

 factor in the progress of geology from iSig, when 

 the problem was first raised by Macculloch, until it 

 was closed in 1SS4 by Sir Archibald Geikie's announce- 

 ment in Nature (vol. xxxi., p. 29) that the generally 

 accepted view could no longer be maintained. The 

 N.\TURE article — perhaps the most sensational an- 

 nouncement in geological literature — was followed in 

 1SS8 by a report from six members of the Scottish 

 Geological Surve}' (Messrs. Peach, Home, Gunn, 

 Clough, Hinxman, and Cadell), giving a summary of 

 the evidence which they had collected as to the struc- 

 ture of the north-western Highlands; and it has taken 

 another twenty years to complete the survey of the 

 whole overthrust region and prepare the detailed 

 observations for publication. The full results are now 

 issued in an elaborate monograph, the most important 

 and the cheapest publication ever issued by the British 

 Geological Survey. It includes 700 crowded pages, 

 52 artistic and instructive plates, and a beautiful 

 colour-printed geological map of the whole area on 

 the scale of four miles to the inch. The price of the 

 book is los. 6rf. The Survey is to be congratulated 

 on having secured for this memoir a style of produc- 

 tion far superior to the usual standard, and on its 

 issue at a price which should ensure for it a wide 

 circulation. 



The book no doubt suffers from the inevitable com- 

 promise between conflicting requirements. Many 

 readers will never have the opportunity of visiting 

 north-western Scotland, and they will seek in this 

 volume for a clear stateinent of the general results ; 

 their needs are satisfied by the fine photographic 

 plates of the scenery, which show the overthrust 



' Memoirs of the Geological Survev of Great Britain. The Geological 

 .Structure of the North-west Highlands of Scotland. By B. N Peach. John 

 Home, the la'e W. Gunn. C. T. Clough and L. Hinxman. with Petrological 

 Chapters and Notes by J. J. H. Te.all. F.Hited bv Sir A. Geikie. Pp. 

 xviii + 668; plates Hi., map. (Glasgow:- H.M. Stationery Office, 1907.) 

 Price 10*. 6(i. 



NO. T995, VOL. 77] 



structures more clearly than they are often visible 

 through the persistent mists of the west Highland 

 hills, and by the masterly introductory statements by 

 Dr. Home in chapters i., iii., xxxii., and xl. (of the 

 last of which Dr. Teall is joint author), and the corre- 

 sponding chapters by Hinxman on the Torridonian, 

 and by Home and Peach on the Cambrian. The 

 memoir has also to serve as a field handbook to those 

 who can visit the district. Accordingly it has to give 

 precise information, which cannot be too detailed, as 

 to localities and sections. The bulk of the book con- 

 sists of detailed local descriptions, written bv Messrs. 

 Peach, Home, Clough, Hinxman, and the late VV. 

 Gunn, with notes bv Cadell, Greenly, and Harker. 

 A third group of geologists will turn to the volume 

 for help in the investigation of other regions of 

 crystalline schists, for nowhere has so large and com- 

 prehensive an area of these rocks been subjected to 

 such a searching investigation. The conclusions of 

 this work and the most important evidence are given 

 in a detailed account by Dr. Teall of the gneisses, and 

 altered sedimentary rocks associated with them. The 

 appendix includes a list of fossils and fossiliferous 

 localities, a chemical study of the Durness Dolomites 

 by Dr. Pollard, and a full bibliography bv Mr. D. 

 Tait. 



The book therefore combines chapters which can 

 be read with advantage by any geological student 

 and others which have to be judged as a collection of 

 materials for reference by specialists. The memoir is 

 appropriately edited by Sir Archibald Geil-cie, who 

 started the work in 1SS3, and carefully supervised its 

 progress for eighteen years, until his retirement from 

 the Survey in igoi. It is doubtless due to his literary 

 skill and sense of proportion that the book enjoys a 

 greater uniformity in style and treatment than would 

 be expected in a work extending over so manv vears, 

 and written by so many men. 



The history of the north-west Highlands controversy 

 is summarised in a chapter by Dr. Home, who lucidly 

 states the results of all previously published geological 

 work on the district. The geological interest of the 

 area dates from the announcement by Mact-uUoch, in 

 iSiq, of his discovery of fossiliferous rocks lying above 

 gneisses, and covered by the gneisses and schists that 

 form the great bulk of the Scottish Highlands. Mur- 

 chison, with his keen scent for a good clue, visited the 

 area, and he re-e.xamined it after the discovery by C. 

 Peach, in 1854, of the better fossils (now known to 

 be Cambrian) in the Durness limestones. Murchison 

 was convinced that the fossiliferous rocks were covered 

 by the eastern gneisses, and, in accordance with the 

 law of superposition, accepted the eastern gneisses as 

 vounger than the rocks beneath them. He regarded 

 the fossils as Lower Silurian, and therefore did not 

 shrink from the apparently inevitable corollary that 

 most of the crystalline rocks of the Scottish High- 

 lands are post-Lower Silurian in age. This conclu- 

 sion had a world-wide influence. Similar crystalline 

 schists form vast regions in all the continents, and 

 thev were at first regarded as all pre-Pateozoic ; but 

 if the Scottish schists are altered Palaeozoic sediments, 

 then the similar rocks elsewhere may include rocks 

 of anv geological age. To this day vast regions of 

 schists and gneisses are mapped as altered Silurian, 

 in consequence of Murchison 's work on the north-west 

 Hiirhlands. 



Murchison 's views were at once opposed. The 

 common-sense judgment of James Nicol showed him 

 the improbability of Murchison 's conclusions, and his 

 keen and careful field-work revealed that the super- 

 imposing of schists over sediments was not an original 

 arrangement, but was due to subsequent earth move- 

 ments. The first controversy was. short. Nicol's inter- 



